The present invention relates to current sensing in a LLC resonant converter, and more particularly, to an LLC resonant converter using lossless current feedback.
Resonant converters are used in high voltage applications where high frequency operation and low switching losses are desired. Common resonant converter topologies include the LC series resonant converter and the LLC resonant converter which is a modified LC series resonant converter including a shunt inductor across the transformer primary winding. The LLC resonant converter has many advantages over the LC series resonant converter. For instance, the LLC resonant converter can regulate the output voltage over wide line and load variations with a relatively small variation of switching frequency. The LLC resonant converter can also achieve zero voltage switching over the entire operating range which improves efficiency.
In the conventional LLC resonant converter, the switching frequency of the converter is regulated by a voltage feedback loop, typically implemented using an opto-coupler transistor to sense the output voltage. Sensing the output voltage for feedback control often results in power loss.